1. Field of the Invention
The present invention relates to an exhaust device of an internal combustion engine.
2. Description of the Related Art
In the related art, in a diesel engine, particulate contained in the exhaust gas is removed by arranging a particulate filter in the engine exhaust passage, using that particulate filter to trap the particulate in the exhaust gas, and igniting and burning the particulate trapped on the particulate filter to regenerate the particulate filter. The particulate trapped on the particulate filter, however, does not ignite unless the temperature becomes a high one of at least about 600xc2x0 C. As opposed to this, the temperature of the exhaust gas of a diesel engine is normally considerably lower than 600xc2x0 C. Therefore, normally an electric heater is used to heat the exhaust gas to ignite and burn the particulate trapped on the particulate filter.
Further, when burning particulate trapped on the particulate filter, if the flow rate of the exhaust gas passing through the particulate filter is too fast, the particulate will not continue to be burned. To make it continue to burn, it is necessary to slow the flow rate of the exhaust gas passing through the particulate filter. Further, to make the exhaust system of the engine more compact, it is preferable to arrange a particulate filter and electric heater in the silencer.
Therefore, known in the art has been an exhaust device providing a particulate filter and electric heater in a silencer, providing a flow path switching valve for switching the flow path of the exhaust gas, using the flow rate switching valve to normally cause the exhaust gas to flow into the particulate filter, heating part of the exhaust gas by the electric heater when igniting and burning the particulate trapped on the particulate filter, then causing the exhaust gas to flow in the opposite direction to the time of normal operation in the particulate filter so as to cause the exhaust gas to be exhausted into the atmosphere without allowing the remaining large part of the exhaust gas to flow into the particulate filter (Japanese Unexamined Utility Model Publication (Kokai) No. 1-149515).
On the other hand, the particulate trapped on the particulate filter is preferably ignited and burned by the heat of the exhaust gas without using an electric heater. Therefore, it has been necessary to reduce the ignition temperature of the particulate. It has been known in the related art, however, that the ignition temperature of particulate can be reduced if carrying a catalyst on the particulate filter. Therefore, known in the art are various particulate filters carrying catalysts for reducing the ignition temperature of the particulate.
For example, Japanese Examined Patent Publication (Kokoku) No. 7-106290 discloses a particulate filter comprising a particulate filter carrying a mixture of a platinum group metal and an alkali earth metal oxide. In this particulate filter, the particulate is ignited by a relatively low temperature of about 350xc2x0 C. to 400xc2x0 C., then is continuously burned.
Summarizing the problem to be solved by the invention, in a diesel engine, when the load becomes high, the temperature of the exhaust gas reaches from 350xc2x0 C. to 400xc2x0 C., therefore with the above particulate filter, it would appear at first glance that the particulate could be made to ignite and burn by the heat of the exhaust gas when the engine load becomes high. In fact, however, once a large amount of particulate ends up depositing on the particulate filter, the particulate gradually changes to hard-to-burn carbon. As a result, even if the temperature of the exhaust gas reaches from 350xc2x0 C. to 400xc2x0 C., sometimes the particulate will not ignite. Therefore, in order to cause the particulate on the particulate filter to continuously burn, it is necessary to prevent a large amount of particulate from depositing on the particulate filter.
An object of the present invention is to provide a compact, practical exhaust device of an internal combustion engine suitable for continuously oxidizing and removing the particulate on the particulate filter.
According to the present invention, there is provided an exhaust gas purification apparatus of an internal combustion engine comprising a silencer body having an end portion and an exhaust gas inflow opening through which an exhaust gas is introduced into an interior of the silencer body; an exhaust gas flow passage having opposing ends and a passage portion extending within the interior of the silencer body, a first exhaust gas inflow-outflow opening being formed at one of the opposing ends of the exhaust gas flow passage, a second exhaust gas inflow-outflow opening being formed at the other of the opposing ends of the exhaust gas flow passage, all of the exhaust gas inflow opening, the first exhaust gas inflow-outflow opening, and the second exhaust gas inflow-outflow opening being arranged in the end portion of the silencer body; a particulate filter arranged in the passage portion of the exhaust gas flow passage; and a flow path switching valve device arranged in the end portion of the silencer body for causing an exhaust gas, discharged from the engine and directed to the silencer body, to selectively flow into at least one of the exhaust gas inflow opening, the first exhaust gas inflow-outflow opening, and the second exhaust gas inflow-outflow opening.